Electric induction apparatus



Feb. 22, 1949. H. w. LORD ,65

ELECTRIC INDUCTION APPARATUS Filed June 12, 1944 inventor: /4 T Harold W. Lord,

His Attorney.

Patented Feb. 22, 1949 ELECTRIC INDUCTION APPARATUS Harold W. Lord, Schenectady, N. Y., assignor to General Electric Company, a corporation of New York Application June 12, 1944, Serial No. 539,975

12 Claims. 1

My invention relates to electrical induction apparatus, and although not limited thereto it has particular application to transformers for use in the communication field.

In th operation of certain tubes in high frequency communication circuits a pulse voltage is impressed between the anode and cathode, and ,a small voltage is also impressed on the heater filament. In supplying the filament power to such electron tubes, since the pulse impressed on the cathode is many times higher than the relatively low voltage needed to provide a filament heater supply, it is desirable to feed the pulse and the filament heater supply to the electron tube through a single transformer so as to eliminate the need of a high voltage low capacity insulated secondary filament transformer. An arrangement for accomplishing this includes a twin secondary winding, and in the conventional transformer for this application the secondary winding is insulated from the primary by the insulation required to withstand the voltage for which the transformer is designed.

It is desirable in pulse transformer applications to have a minimum leakage reactance between the primary and secondary windings as well as a minimum distributed capacitance. An auto transformer would have a minimum leakage reactance between the primary and secondary but in an auto transformer the primary and secondaries are not isolated so that filament current cannot conveniently be supplied through the secondary without being short circuited by the primary.

It is therefore an object of my invention to provide a transformer with electrically isolated primary and secondary windings which will have a'minimum leakage inductance and distributed capacitance.

A further object of my invention is to provide a transformer having particular application to high frequency communication circuits which will havea minimum leakage inductance and distributed capacitance.

A further object of my invention is to provide a transformer with a plurality of windings which has a. small mean length and so as to provide a minimum distributed capacity.

Further objects and advantages of my invention will become apparent from the following description referring to the accompanying drawing, and the features of novelty which characterize my invention will be pointed out with particularity in the claims annexed to and forming a part of this specification.

In the drawing, Fig. 1 is a sectional side elevation of an electric induction apparatus which is provided with an embodiment of my invention; Fig. 3 is a sectional side elevation illustrating the relationship of the core and coils of a modification of the construction of Fig. l, and Fig. 2 illustrates schematically the coils of the apparatus in Fig. 1.

In the arrangements illustrated in the drawing I have shown a transformer having particular application as a pulse transformer but itis to be understood that the features of my invention may be employed in any other suitable type of electrical induction apparatus. In order to feed both the filament heater current and the pulse to a tube through a transformer which has minimum leakage inductance and distributed capacitance, I provide a transformer having two winding legs with a primary winding having sections on each of the legs. Two secondary windings are provided each having a plurality of sections with one section of each of the secondary windings being closely coupled with one of the primary winding sections, and the remaining sections of the secondary winding being distributed around each of the winding legs that the secondary winding circuits progress together up one of the winding legs, and then up the other of the winding legs, the ends of the latter secondary winding sections being connected to. the filament and cathode of the electron tube. This keeps to a minimum voltage stress between windings on opposite legs. 01 course, the windings could progress oppositely if they are properly wound and connected.

Referring more particularly to Fig. 1 of the drawing, I have illustrated a transformer construction l0 for'operating an electron tube H which may be of any suitable type such as an oscillator. In order to feed a heater current as well as a power pulse to the tube H the transformer I0 is provided with a primary winding having sections l2 and I3 and secondary windings each of which have a plurality of sections. In order to facilitate the tracing of. the various winding sections it will be noted that the primary winding sections l2 and I 3 are indicated by cross hatching lines 30 degrees from the horizontal. Ends of the sections are connected together to provide a terminal l4 and the'other ends being connected together and grounded at i5. With adjacent ends grounded it will be understood that the primary winding sections are wound in opposite directions. One of the secondary windings is provided with sections it and I! which are on the same core leg l8 as the primary winding l2. A third section IQ of the first secondary winding surrounds another core winding leg 20 which is the same leg as is surrounded by primary winding section l3. Similarly a second secondary winding is provided having sections 2! and 22 which surround the winding leg 20 and a third section 23 which surrounds the winding leg i8. In order to facilitate the identification of the secondary windings the first secondary winding which is made up of the sections i6, i1, and 19 are cross hatched with lines 60 degrees from the horizontal, while the second secondary winding whichis made up of in the construction illustrated in Fig. 1, it will be I noted that the primary winding section 2 is interwound with the secondary winding section It of the first secondary winding. Similarly, primary winding section I3 is interwound with the secondary section winding 2| of the second secondary winding. In order to further insure that the impulse voltage which is impressed across the primary winding will not produce a differential of voltage between the corresponding portions of the various sections of the first and second secondary windings a second pass of each of the secondary windings progresses similarly up one of the winding legs while the third pass of each of the secondary windings progresses similarly up the other of the winding legs. Thus when a secondary winding .25 of a filament transformer is connected to the first and second secondary winding sections, lines 26 and 21 which are connected to the other ends of the first and second windings respectively, will have a voltage diiferential therebetween of only the relatively small voltage of the filament heating transformer 25, although the lines 25 and 21 which are connected to the cathode will have the full pulse vpltage between the lines and ground.

Connections between the secondary winding sections are as follows: One end of the first secondary winding section It is connected to one end of the first secondary winding section l9 through a conductor 28. Similarly an end of the second secondary winding section 2| is connected to the second secondary winding section 22 through a conductor 29. It will therefore be seen that each of the winding sections l5 and 2| proresses from one end of the core to the other end of the core in the same manner, that is from right to left in Fig. 1, while the second pass including the sections l9 and 22 progresses in a similar manner. The third pass of the secondary windings is provided by the sections l1 and 23, and it will be seen that the secondary winding section I9 is connected to the opposite end of the secondary winding section I! through a conductor 33. Similarly the secondary winding section 22 is connected to the opposite end of the secondary winding section 23 through a conductor 3| and these sections also progress on the winding leg I 8 from right to left in Fig. 1.

In view of the arrangement of secondary windings and their connections as described above. there will be no resultant magnetomotive force to produce a circulating flux in the core due to alternating current flowing in the heater supply circuit from the source 25. Thus in reference to the first passes which includes the secondary winding sections l6 and 2|, the flux in each of the legs l8 and 20 due to current flow through the filament from the source 25 will be as shown by the arrows, and it will be seen that there will be no resultant circulating flux. As to the magnetomotive force produced by alternating current fiow from the source 25 to the heater through the second and third passes of the first and second secondary windings it will be seen that the current flow through adjacent sections on each leg will be in opposite directions so that the magnetomotive force will cancel out.

It will be seen that the construction as illustrated in Fig. 1 facilitates the winding of the various primary and secondary sections, as the winding turns may be formed of conductors of a similar diameter. Thus, for example, with a five to one transformer the primary winding sections l2 and I3 may each be formed with ten turns and r with secondary winding sections l6 and 2| which are interwound with the primary winding sections l2 and I3 also having ten turns. Furthermore by winding the remaining secondary winding see-. tions of twenty turns each of similar size conductor it will be seen that the total step-up effect will be five to one. It will be understood that the insulation between sections l and 23 need be only a few mils, while the insulation between the primary winding sections and sections 22 and 23 may be much larger when my invention is applied to pulse transformers. v

In the construction illustrated in Fig. 1 the close coupling between the primary winding sections and one section of each of the secondary windings is accomplished by interwinding the primary and secondary winding sections, and in Fig. 3 I have illustrated another arrangement for obtaining the relatively close coupling by winding relatively closely with a minimum amount of insulation primary and secondary winding sections. Thus in Fig. 3 the primary winding includes sections 32 and 33 which surround different core legs is and 20 while the first secondary winding has a section 34 wound very close to the section 32 and the second secondary winding has a section 35 which is wound very close to the primary winding section 33. In the construction illustrated in Fig. 3 the secondary winding sections 34 and 35 are wound over the core winding legs l8 and 20 with the primary winding sections 32 and 33 surrounding the secondary winding sections 34 and 35, respectively. Since the winding sections 32 and 34, and 33 and 35 are respectively in approximately the same potential only a minimum amount of insulation need be provided between the adjacent winding sections. The first secondary winding progresses from the winding section 34 to a winding section 36 on the winding leg 20 through a connector 31, while the first section 35 of the second secondary winding progresses to a secondary winding section 38 through a conductor 39. Thus the second pass of the secondary windings will be around the same leg 20 and in the same direction, while the first pass is provided by one section around one leg and the other section around the other leg but progressing in the same direction. The third pass of the secondary windings includes the first and second secondary winding sections 40 and 4| respectively. One end of the first secondary winding section 36 is connected to the opposite end of the secondary winding section 40 through a conductor 42. Similarly one end of the second secondary winding section 38 is connected to the opposite end of the second secondary winding section 4| through a conductor 43. The opposite ends of the secondary winding sections 40 and 4| are connected to the conductor leads 26 and 21 of the tube II in the manner shown in Fig. 1. The magnetomotive force in the secondary winding sections due to current flow through the filament from the filament transformer will cancel out as described above in connection with Fig. 1.

It will be noted that in both Figs. 1 .and 3 one of the two equal voltage secondary windings is more closely coupled to the primary winding than is the other secondary winding. In'both figures the most closely coupled secondary winding is the onev which is connected by lead 21 to the cathode of the electronic valve H. Thus, considering first Fig. 1, it will be seen that although the lowest voltage (relative to ground) sections l6 and 2| of the two secondary windings are respectively interwound with the two primary sections on the different core legs, the intermediate voltage section 22 and the high voltage section 23 which are respectively in series with each other and in series with low voltage section 2i ar both relatively closely coupled to the primary winding as they constitute the two intermediate ones of the three winding layers on each leg, whereas the outer layers l1 and is are connected in series with the low voltage section IE to the terminal 26 which is connected to the cathode heater. correspondingly, in-Fig. 3 the low voltage section or layer 35 and the inter mediate voltage-section or layer 38 surround the primary section 33 and the remaining or high voltage section if is adjacent to the other primary section 40 so that the secondary winding connected to the lead 21 and comprising the windings 35, 38 and ll is more closely coupled to the primary winding than is the other secondary winding constituting the serially-connected sections or layers advantage of this to reduce the losses and hence increase the illciency of the transformer. The loss reduction which I achieve includes both the core loss and the dielectricloss. The latter is a function of the distributed capacitance of the transformer. It is very important in pulse transformers that the losses be as low as possible so that the output pulse of the transformer will corresame rating.

34, and 40, the latter two being the outermost layers of the two legs andthus being the most loosely coupled of all the layers relative to the primary winding. 0

It follows from the above that when a voltage pulse is impressed between primary terminal I4 and ground in either Fig. 1 or Fig. 3 most of the high voltage secondary current will flow through the high voltage closely coupled secondary winding which is shown connected directly to the peded by having to flow through the cathode heater. The less closely coupled secondary winding in effect is essentially a return path for the oathode heater current. As both secondary windings have equal and opposite voltage in the loop circuit which includes them and which is completed by the cathode heater and the secondary winding 25 of the cathode heater supply transformer, no circulating current is introduced by the connection of this return path effectively across the more closely coupled secondary winding. In other words, the less closely coupled secondary winding, having a voltage equal to the more closely coupled secondary winding, does not in any way tend to act as a short circuit or even a partial short circuit for the more closely coupled secondary winding.

In conventional pulse transformers in which the supply of filament or cathode heating power is fed up through twin secondary windings on the transformer, which secondary windings are insulated from the primary winding, these secondary windings are interwound with each other and are not interwound, or specially close coupled, with the primary winding. In the present transformer a part of each secondary winding is specially close coupled with the primary winding. This, therefore, permits a looser coupling of the rest of the secondary winding relative to the primary winding than in conventional pulse transformers without increasing the over-all leakage reactance of the transformer. I therefore take cathodeso that this current flows directly through a the electrodes of the tube ll without being im- Although I have shown and described particular embodiments of my invention, I do not desire to be limited to the particular embodiments described, and I intend in the appended claims to cover all modifications which do not depart from the spirit and scope of my invention.

. What I claim as new and desire to secure by Letters Patent of the United States is:

1. An electric induction apparatus including a core having a pair of winding legs, a primary winding having a pair of primary winding sections with each section around a different one of said core winding legs, and two secondary wind- 40 ing around the other of said legs so that each leg has three secondary sections of which one is part of one secondary winding and the other two are part of the other secondary winding.

2. An electric induction apparatus including a core having a pair of winding legs, a primary winding having a pair of primary winding sections with each section around a different one of said core winding legs, and two secondary windings each having at least three serially connected sections with one of said sections of, each secondary winding around a different one of said winding legs and the remaining of said sections of each secondary winding around the other of said legs so that each leg has three secondary sections of which one is part of one secondary winding and the other two are part of the other secondary winding.

3. An electric induction apparatus including a pair of interconnected primary winding sections, two secondary windings with each of said secondary windings having at least three serially connected winding sections, a core member having two winding legs, said secondary winding sections being distributed with one section of each of said secondary windings around a different one of said core winding legs, and the remaining two sections of each of said secondary windings being around the other winding leg so that each leg has three secondary sections of which one is part of one secondary winding and the other two are part of the other secondary winding.

4. An electric induction apparatus including a core having first and second winding legs, first and secondary primary winding sections, first second, and third winding sections, one of said primary winding sections and said first section of said first secondary winding surrounding one leg, said second primary section and said first section of said second secondary winding surrounding said second winding leg, said second sections of said first and second secondary windings surrounding said second core winding leg, and said third sections of said first and second secondary windings surrounding said first core winding leg.

5. A transformer having a primary winding and two equal voltage secondary windings, both of said secondary windings having a plurality of sections which aredifierently coupled to said primary winding where by one of said secondary windings is more closely coupled to said primary winding than the other one, said more closely coupled secondary winding having a section which is more loosely coupled to said primary winding than the most closely coupled section of the other secondary winding.

6. A transformer comprising, in combination, a two-legged core, three winding layers on each of said legs, the inner layer on each leg being two equal interwound insulated sections, two of said sections which are on difierent legs being interconnected to constitute the primary winding of said transformer, the other two sections being sections respectively of two secondary windings of said transformer, the intermediate winding layers on said legs being serially connected with each other and with one of said interwound secondary winding sections on an inner leg to constitute a closely coupled secondary winding, the outer winding layers of said legs being serially connected with each other and with the remaining interwound inner layer secondary winding section to constitute a less closely coupled secondary winding.

7. A 5-to-1 ratio voltage step-up pulse transformer for a hot cathode electronic valve comprising, in combination, a two-legged core, three equal turn equal conductor size winding layers on each of said legs, the inner layer on each leg being two equal interwound insulated sections, two of said sections which are on different legs being interconnected 'to constitute the primary winding of said transformer, the other two sections being low voltage sections respectively of two secondary windings, said low voltage sections each having a terminal for connection to the secondary winding of a low voltage low capacity cathode heating current supply transformer, the intermediate winding layers on said legs being serially connected with each other and with one of said low voltage sections to constitute a closely coupled secondary winding having a high voltage terminal for connection to the cathode of an electronic valve, the outer winding layers on said legs being serially connected with each other and with the other low voltage section to constitute a return path of equal voltage to said closely coupled secondary winding for cathode heater current and having a high voltage terminal for connection to a heater for said cathode.

8. A transformer comprising, in combination, a. two-legged core, four winding layers on each of said legs, two of said layers which are on different legs being interconnected to constitute the primary winding of said transformer, one of said primary winding layers being an intermediate layer, the two winding layers which are directly adjacent to but inside and outside of said intermediate layer being serially connected with each other and with a layer which is adjacent the other primary winding layer to constitute a relatively closely coupled secondary winding, the three re- 6 mainin'g layers being serially connected to constitut a less closely coupled secondary winding.

9. A 3-to-1 ratio voltage step-11D pulse transformer for a hot cathode electronic valve comprising, in combination, a two-legged core, four equal turn equal conductor size winding layers on each of said legs, the two innermost layers constituting low voltage sections of two difierent secondary windings each of which has a terminal for connection to a low voltage low capacity cathode heating current supply transformer, the two next outermost layers on the difierent legs being connected in parallel to constitute the primary winding of said transformer, the two next outermost layers on the different legs being serially connected with each other and with one of the innermost layers to constitute a closely coupled high voltage secondary winding having a terminal for connection to the cathode of an electronic valve, the two outermost layers being serially connected with each other and with the Other innermost layer to constitute a less closely coupled high voltage secondary winding having a terminal for connection to a heater for said cathode.

- 10. A transformer having a pair of insulated windings with a voltage ratio of Rzl where R is greater than 1, the lower voltage winding of said transformer and a l/R part of the high voltage winding being interwound, the remaining part of the higher voltage winding being separately wound.

11. A transformer comprising, in combination, a core with a winding leg, a one-layer low voltage winding and a multi-layer high voltage winding on said leg, said windings being insulated from each other, said layers being concentric, the low voltage winding layer and one of the high voltage winding layers being coextensive.

12. A transformercomprising, in combination,

a core having a winding leg, a low voltage winding and two high voltage windings on said leg, said windings being insulated from each other, saidwindings being in separate concentric layers, said low voltage winding being in one of the high voltage winding layers.

HAROLD w. LORD.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number 

